I qualified for my first block in June 2022. At the time you had the option to fill out a form and have it mailed to your house.
Despite several conversations with the LA on board various cruises, we didn't get that first block until March 2024 (when we were half way to block #3). And that was after that ship's LA contacted shore side and was told too much time had passed and we were out of luck to get a block for the ship we were on when we earned it. The LA nicely just gave us one he had for the current ship. So our first block, earned on Serenade, is a block for Adventure.